High strength camfer on quartzware

ABSTRACT

A structural member for use in extremely high temperature environments that has substantially flat exterior for resting on a flat surface. The substantially flat exterior of the structural member has a low angle chamfer that is preferably less than 45 degrees and that rises far enough above the flat surface so that when the edge is rolled using conventional processing methods, the resulting high point does not extend a distance far enough to contact with the surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. provisional patent applicationSer. No. 61/111,683, filed on Nov. 5, 2008.

TECHNICAL FIELD

This invention relates to a structural member for use in extremely hightemperature environments such as those found during the processing andmanufacture of silicon wafers and the like.

BACKGROUND OF THE INVENTION

Durable and strong structural members for use in extremely hightemperature environments, such as a range between 900 degrees Celsius to1500 degrees Celsius, are used in a wide variety of applications. Forexample, in the semi-conductor industry, the manufacture ofsemi-conductors from silicon frequently requires heating silicon wafersand the like to within this temperature range.

Usually, the wafers are stacked in a rack-type structure, which isreferred to in the industry as a “boat”, and the rack containing theplurality of wafers is placed in a furnace. The structural membersforming the rack must be sufficiently strong to hold the wafers, even atthese extreme temperatures, without weakening due to the extreme heat.Moreover, it is desirable for the rack to be reusable. Accordingly, themembers forming the rack, the stand on which the rack is placed, and theeven the furnace structures themselves must be sufficiently durable andstrong to withstand numerous heating and cooling cycles.

Structural members operating within these extreme temperatures must beformed with materials having melting points well above the range oftemperatures in which these structural members are expected to operate.Steel and other alloy-based materials commonly used as structuralmembers in lower temperature environments vaporize and/or melt at theseextreme temperatures rendering them useless. Accordingly, knownmaterials for constructing structural members used in such extremelyhigh temperature environments are limited.

Moreover, in cases where a structural member is used in an extremelyhigh temperature to facilitate semi-conductor manufacture, it isimportant that the structural member limit the amount of impuritiesreleased by vaporization during the heating process.

A particularly favorable material used as a structural member in theconstruction of boats for use in semi-conductor fabrication is fusedsilica glass, which is also referred to in the industry as fused quartzand collectively refers to materials containing at least one of a groupof minerals that are commonly referred to as the “SiO₂” group. Thismaterial has a high melting/vaporization point, and can be processed andor selected so as to release few, if any, impurities during the heatingprocess. Moreover, fused silica glass can be formed into structuralmembers, and it can be joined together with other structural members,usually by heat welding, to make a boat or the like.

Despite the benefits of fused silica glass for use as a structuralmember, it has several drawbacks. For example, component parts made fromthese hard materials like Quartz glass are often stacked on top of each.In some cases the interface surfaces of these parts are not completelyflat and smooth. In many cases the product is fire polished on corner oredge to make them smooth. The corner or edge when fire polished “rolls”due to surface tension. As shown in FIG. 1 (PRIOR ART), this rolled edgetends to produce high points (A) along exterior contact surfaces 48′,which are usually referred to as burms or bumps. Often times, all theweight of the stacked parts in the rack (B) is supported by these highpoints A as shown. Accordingly, these points (A) serve as substantialpoints of contact between the boat and the surface the boat rests onduring the extreme temperature heating processes the rack is subjectedto, and these points of contact tend to develop high stress and areprone to breaking and cracking during static and dynamic loading.

In an attempt to reduce or minimize this characteristic, some extremehigh temperature rack manufacturers may chamfer the parts with a 45 degchamfer from 0.2 mm to 1 mm then fire polish the surface and edge.However, these actions still tend to produce high points (A, FIG. 1(PRIOR ART)).

SUMMARY OF THE INVENTION

Accordingly, despite the available structural members for use inextremely high temperature environments, there remains a need for aneconomical thermally resistant, structural member that is more durablethan the known structures, particularly during repeated heating andcooling cycles and that does not have bumps or high points at exteriorcontact surfaces that promote high stress fractures and the like. Inaddition to other benefits that will become apparent in the followingdisclosure, the present invention fulfills these needs.

The present invention is structural member for use in high temperatureenvironments that has substantially flat exterior for resting on a flatsurface. The substantially flat exterior of the structural member has alow angle chamfer that is preferably less than 45 degrees and that risesfar enough above the flat surface so that when the edge is rolled usingconventional processing methods, the resulting high point (burm or bump)does not extend a distance far enough to contact with the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (PRIOR ART) is an enlarged, partial front view of prior artstructural member for use in extremely high temperatures.

FIG. 2A is a front plan view of a structural member for use in extremelyhigh temperatures in accordance with an embodiment of the presentinvention.

FIG. 2B is a top plan view of the structural member of FIG. 2A.

FIG. 2C is an enlarged, partial front plan view of the structural memberof FIG. 2A taken along arrow 2C of FIG. 2A.

FIG. 3 is an enlarged, partial front plan view of a lower surface of thestructural member of FIG. 2A in accordance with an embodiment of thepresent invention.

FIG. 4 is an enlarged, partial front plan view of a lower surface of thestructural member of FIG. 2A in accordance with an alternativeembodiment of the present invention.

FIG. 5 is an enlarged, partial front plan view of a lower surface of thestructural member of FIG. 2A in accordance with a second alternativeembodiment of the present invention.

FIG. 6 is an enlarged, partial front plan view of a lower surface of thestructural member of FIG. 2A in accordance with a third alternativeembodiment of the present invention.

DETAILED DESCRIPTION

A structural member 30 for use in a high temperature environment isdisclosed in FIGS. 2A-6. The structural member 30 is preferably formedof fused silica or the like, which is commonly known in the industry asquartz.

A. Boat Construction

Preferably and referring to FIG. 2A-C, a plurality of structural members30 are joined together using conventional methods to form a heating boat36 used to hold silicon wafers 37 (FIG. 2B) and the like during hightemperature heating in a furnace. The heating boat 36 can include aplurality of elongate structural members 30 aligned substantiallyparallel to teach other and joined at their respective ends by an uppermember 38 and a lower member 40.

A plurality of spaced-apart notches 42 is preferably provided along eachstructural member 30. Preferably, the notches 42 in each structuralmember 30 are aligned substantially horizontally to form substantiallyhorizontal rows 44 of like notches 42 within the structural members 30.Accordingly, a silicon wafer 37 (FIG. 2B) may be secured to the heatingboat 36 by being placed within one of the rows 44 of notches 42. Morepreferably, a plurality of silicon wafers may be secured to the heatingboat 36 and spaced-apart from each other by being placed in separaterows 44 of notches 42 on the structural members 30.

As best shown in FIG. 2A, the upper and lower members 38, 40 arepreferably planar and have a substantially circular shape. Preferably,three structural members 30 are joined to the upper and lower members38, 40 and spaced apart from each other as shown so as to allow asilicon wafer 37 (FIG. 2B) to be easily inserted and removed through anopen side 46 formed thereby.

B. Surface Engaging Structure

More preferably, the lower exterior side 48 of the lower member 40 has asurface engaging structure 100 configured as shown in one of theembodiments of FIGS. 2A, 2C, and 3-6. Preferably, a low angle chamferwith and angle {acute over (α)} that is less than 45 degrees is providedso that the chamfer will rise far enough above the surface the lowermember 40 rests on so that when the edge is rolled the high point 110(burm or bump) does not extend a distance 142 (FIG. 6) so as to contactthe surface. At the intersection 104 of the low angle chamfer and theprimary surface 100 there is an intersection point 104. Preferably, alarge radius 112 about this intersection point 104 is provided. Thisradius 112 reduces the effects of any bump or burm 110 arising from thefire polishing process. More preferably, the chamfer extends a distance140 (FIG. 6) that is 2 to 5 millimeters from the outer edge of themember 40.

The foregoing steps will result in a surface engaging structure 100 witha fire polished surface 48 that has greatly reduced rolled bumps andwill result in a less facture prone interface of mating surfaces.

Having here described preferred embodiments of the present invention, itis anticipated that other modifications may be made thereto within thescope of the invention by individuals skilled in the art. Thus, althoughpreferred, more preferred, and alternative embodiments of the presentinvention have been described, it will be appreciated that the spiritand scope of the invention is not limited to those embodiments, butextend to the various modifications and equivalents as defined in theappended claims.

1. A structural member for use in extremely high temperatureenvironments having: a frame having an upper surface and a lowersurface; said lower surface having a substantially planar exteriorengaging surface and an outer edge; a chamfer extending from saidsubstantially planar exterior engaging surface toward said outer edge bya defined distance away from said exterior engaging surface at saidouter edge such that when the lower surface is fire polished resultingburms along said outer edge are shorter than said defined distance. 2.The structural member of claim 1, wherein said structural member is aboat for heating silicon wafers therein.
 3. The structural member ofclaim 1, wherein said structural member is formed of materials selectedfrom SiO₂ group.
 4. The structural member of claim 3, wherein saidstructural member is formed of fused silica.
 5. The structural member ofclaim 1, wherein said chamfer extends inwards from said outer edge by asecond defined distance.
 6. The structural member of claim 5, whereinsaid second defined distance is between 2 to 5 millimeters.
 7. Thestructural member of claim 1, wherein said defined distance is between0.25 to 2 millimeters.
 8. The structural member of claim 1, furtherincluding a radius transitioning from said lower to said chamfer.
 9. Thestructural member of claim 8, wherein said radius is large.
 10. Thestructural member of claim 1, wherein said chamfer angle is less than 45degrees.